The present invention relates to a toroidal continuously variable transmission for a vehicle, and specifically to a link support structure of a toroidal continuously variable transmission.
To meet demands for increased shift comfort, improved driveability, and reduced fuel consumption and exhaust emissions, there have been proposed and developed toroidal continuously variable transmissions often abbreviated to xe2x80x9ctoroidal CVTsxe2x80x9d, in which a transmission ratio is steplessly variable within limits. On such toroidal CVTs, engine power (torque) is transmitted from an input disk to an output disk via a traction oil film formed between a power roller and each of the input and output disks, using a shearing force in the traction oil film at high contact pressure. The input and output disks coaxially oppose each other. Generally, a pair of power rollers are disposed between the input and output disks. One such toroidal CVT has been disclosed in Japanese Patent Provisional Publication Nos. 9-317837 (hereinafter is referred to as JP9-317837 corresponding to U.S. Pat. No. 5,893,815) and JP2001-182793 (corresponding to U.S. Patent Publication No. US2001/0016534 A1). FIG. 8 shows a partial cutaway view of the front side of a so-called double cavity type toroidal CVT (disclosed in JP9-317837 corresponding to U.S. Pat. No. 5,893,815) that a first variator (a front toroidal CVT mechanism) and a second variator (a rear toroidal CVT mechanism) are set in tandem and coaxially arranged in the interior space of a toroidal CVT casing 1. As shown in FIG. 8, the front toroidal CVT mechanism has a pair of trunnions 14, 14 each serving as a power roller support for power roller 8 being in contact with a torus surface of each of the input and output disks under preload (under a loading force). In FIG. 8, the axis denoted by O1 is a common rotation axis of the input and output disks, the axis denoted by O2 is a trunnion axis, and the axis denoted by O3 is a rotation axis of the power roller. Owing to the grip force (the loading force) acting on the power roller, there is a tendency for the power roller to be driven out from between the input and output disks. To avoid this, upper ends of trunnions 14 are mechanically linked to each other by means of an upper link 16, while lower ends of trunnions 14 are mechanically linked to each other by means of a lower link. FIGS. 9 and 10A-10B show a conventional link support structure as disclosed in JP9-317837 (corresponding to U.S. Pat. No. 5,893,815) or U.S. Pat. Publication No. US2001/0016534 A1. As clearly shown in FIG. 9, upper link 16 is formed therein with two pairs of trunnion support holes h1, h1, h1, h1, each pair h1, h1 associated with the two trunnions included in one of the first and second variators. A substantially square hole h2 is formed in the upper link and located midway between upper-left and lower-left trunnion support holes h1, h1, supporting the trunnion pair 14, 14 included in the first variator. In the same manner, a substantially square hole h2 is formed in the upper link and located midway between upper-right and lower-right trunnion support holes h1, h1 supporting the trunnion pair 14, 14 included in the second variator. Upper link 16 is pivotally supported by way of a pair of link posts or a pair of link supports 11, 11, passing through the respective square hole h2, h2. In FIG. 9, reference sign h3 denotes a central rectangular hole, which is provided to avoid the interference between the upper link and the output disks of the first-and second variators. Link support 11 is securely connected to toroidal CVT casing 1 by means of a bolt A. Concretely, upper link 16 is pivotally supported by way of two pairs of pins 12a, 12a, 12a, 12a, which are aligned with each other in the direction of common rotation axis O1 of the input and output disks. The lower link support structure is the same as the upper link. FIG. 10A is a side view of the upper link portion, taken in the direction of common rotation axis O1 of the input and output disks. FIG. 10B shows analytical mechanics (vector mechanics) for a force xcex3 applied from the right-hand trunnion to the upper link and a reaction force xcex4 applied from the left-hand trunnion to the upper link and a force xcex5 applied to pin 12a, during transmission-ratio changing. As is generally known, during ratio changing, in order to obtain a desired transmission ratio determined based on the magnitude of a gyration angle of the power roller, each power roller is vertically shifted or displaced from a neutral position (anon-ratio-changing position shown in FIG. 10A) at which power-roller rotation axis O3 intersects the center of rotation (common rotation axis O1) of the input and output disks. The shifting operation of the power roller pair is created by shifting one of the trunnion pair 14, 14 in a first direction xcex1 of trunnion axis O2 perpendicular to power-roller rotation axis O3 via a hydraulic servo mechanism with a servo piston, and by shifting the other trunnion in a second direction xcex2 opposite to the first direction xcex1 via a hydraulic servo mechanism in synchronism with the shifting operation of the one trunnion. That is, the two trunnions are shifted in phase in the opposite trunnion-axis directions xcex1 and xcex2 during ratio changing. A jointed portion between each of the trunnions and the upper link must be designed to permit the previously-noted vertical displacement or offset of the power roller from the neutral position and a change of the gyration angle of the power roller. Thus, as shown in FIGS. 10A and 10B, the jointed portion is constructed as a combination joint comprised of a bearing B fitted to the upper end portion of trunnion 14 and a spherical joint C fitted onto the bearing B. As best seen in FIG. 9, the conventional link support structure is a pin-support structure composed of pins 12a, 12a, 12a, 12a axially aligned with each other in the direction of common rotation axis O1. In case of such a pin-support structure, pins 12a, 12a, 12a, 12a function to restrict translating motions in three different directions, namely a longitudinal direction along common rotation axis O1 of the input and output disks, a vertical direction along trunnion axis O2, and a lateral direction (a left-and-right direction) normal to both the longitudinal direction along input/output-disk rotation axis O1 and the vertical direction along trunnion axis O2. The conventional pin-support structure has several drawbacks discussed hereunder.
As can be seen in FIG. 10B, during ratio changing that trunnions are shifted in phase in the opposite directions xcex1 and xcex2, there is a tendency that trunnion 14 is relatively inclined with respect to upper link 16 with an intersection angle, which is an angle of deflection at the intersection point between the straights of the upper link and the trunnion. Assuming that the right-hand trunnion of FIG. 10B is brought into spot-contact with the upper link at an interference point or a contact point f with an intersection angle during ratio changing, a force xcex3 acts on the upper link via contact point f. In case of the pin-support structure that the central portion of the upper link is pin-connected to toroidal CVT casing 1, pin 12a serves as a fulcrum point of a lever, contact point f serves as a power point (or a point of application), and a frictional contact portion between the inner peripheral wall surface of the support hole of upper link 16 and a combination joint (in particular, a spherical joint C) of a jointed portion between the left-hand trunnion of FIG. 10B and upper link 16 serves as a point of action. Owing to force xcex3 acting on the upper link via contact point f, a reaction force xcex4 acts on the frictional contact portion (serving as a point of action) between upper link 16 and the left-hand trunnion. On the other hand, pin 12a (serving as a fulcrum point of a lever) receives a resultant force xcex5 of forces xcex3 and xcex4. Note that, according to the principle of action and reaction, a force, which has the same magnitude as the force xcex3 and acts in the direction opposite to the direction xcex2, reacts on the right-hand trunnion, and a force, which has the same magnitude as the force xcex4 and acts in the direction opposite to the direction xcex1, acts on the left-hand trunnion. As appreciated from the analytical mechanics of FIG. 10B, the forces xcex3 and xcex4 act in the same direction of trunnion axis O2. However, with respect to the circumferential direction of the input disk or the output disk, the direction of act of force xcex3 is opposite to that of force xcex4. For the reasons discussed below, the forces xcex3 and xcex4 acting opposite to each other with respect to the circumferential direction of the input disk or the output disk, leads to the problem of a deterioration in torque distribution or torque allotment between a pair of power rollers 8, 8 included in each variator. In other words, forces xcex3 and xcex4 acting on the contact points cause a torque difference between the torque flowing through one of power rollers 8, 8 and the torque flowing through the other power roller, thereby resulting in an undesired slip (power loss) at the frictional engagement portion between the power roller and each of the input and output disks. The torque flowing through the power roller is calculated as the product of the distance (called xe2x80x9cinput contact radiusxe2x80x9d) from a contact point between the power roller and the input disk to input/output-disk rotation axis O1 and a force acting on the frictional engagement portion between the power roller and the input disk, or calculated as the product of the distance (called xe2x80x9coutput contact radiusxe2x80x9d) from a contact point between the power roller and the output disk to common rotation axis O1 and a force acting on the frictional engagement portion between the power roller and the output disk. To avoid or reduce the undesired slip, the grip force (the loading force) of the power roller must be increased. Taking into account the torque flow from the input disk via the power roller to the output disk, from the viewpoint of the vector analysis, a first force is applied from the input disk to the first frictional engagement portion of the power roller, and simultaneously a second force (a reaction force) is applied from the output disk to the second frictional engagement portion diametrically opposed to the first frictional engagement portion with respect to power-roller rotation axis O3. In other words, during power transmission via the power roller, the trunnion (the power roller support) receives both the first and second forces, (in other words, twice the first force, because the magnitudes are the same in the first and second forces). The first and second forces have the same magnitude and act in the same sense or direction, that is, in the radial direction of the power roller. Thus, the resultant force of the first and second forces will be hereinafter referred to as xe2x80x9cradial forcexe2x80x9d acting on the power roller. When maintaining the neutral position (the non-ratio-changing position), the same magnitude of hydraulic pressure applied to each servo piston of the trunnion pair is balanced to the radial force acting on the power roller. By way of Pascal""s principle, the hydraulic pressure applied to the left-trunnion servo piston is adjusted to be equal to the hydraulic pressure applied to the right-trunnion servo piston. Ratio changing is achieved by increasing or decreasing the hydraulic pressure, applied to each servo piston, from the hydraulic pressure level corresponding to the radial force acting on the power roller. An upshift occurs by increasing the hydraulic pressure. In contrast, a downshift occurs by decreasing the hydraulic pressure. In presence of the previously-noted forces xcex3 and xcex4 having almost the same magnitude but different sense with respect to the circumferential direction of the input/output disk, there is a tendency for the hydraulic pressure applied to the servo piston to be unbalanced to the radial force acting on the power roller. This deteriorates torque distribution between a pair of power rollers 8, 8 included in each variator. If a comparatively large torque is allotted to one of the two power rollers included in each variator due to such a deteriorated torque distribution, there is an increased tendency for the one power roller to slip. To avoid this, the grip force (the loading force) must be increased. This leads to the problem that a mechanical strength of each toroidal CVT part is enhanced and thus the toroidal CVT is large-sized. Additionally, the conventional toroidal CVT uses the complicated pin-support structure as described previously. This leads to the problem that the number of parts constructing the toroidal CVT increases. Manufacturing costs also increase. Additionally, due to an increase in the loading force, the rigidity of each of the upper and lower links must be enhanced. In case that square hole h2 is formed in the upper link (or in the lower link) and located midway between support holes h1, h1 supporting the trunnion pair 14, 14, the rigidity of each of the upper and lower links must be further enhanced. This leads to the problem that the thickness of the upper or lower link must be further increased.
Accordingly, it is an object of the invention to provide a toroidal continuously variable transmission having an improved link support structure, which avoids the aforementioned disadvantages.
In order to accomplish the afore mentioned and other objects of the present invention, a toroidal continuously variable transmission comprises input and output disks opposed to each other and coaxially arranged on a common rotation axis, a plurality of power rollers interposed between the input and output disks under axial preload for power transmission, a plurality of trunnions rotatably supporting the respective power rollers to permit a tilting motion of each of the power rollers about a trunnion axis perpendicular to a power-roller rotation axis for ratio changing, an upper link that mechanically links upper ends of the trunnions to each other, a lower link that mechanically links lower ends of the trunnions to each other, a transmission casing, a link support structure that supports one of the upper and lower links in the transmission casing, the link support structure comprising a stationary portion fixed to an inner periphery of the transmission casing, and an engagement portion formed at the one link and in engagement with the stationary portion to provide an engagement pair, the engagement pair restricting a fore-and-aft movement of the one link relative to the transmission casing in a fore-and-aft direction along the common rotation axis, and a freedom for the fore-and-aft movement of the one link relative to the transmission casing being relatively less than a freedom for a vertical movement of the one link relative to the transmission casing in a vertical direction along the trunnion axis and relatively less than a freedom for a left-and-right movement of the one link relative to the transmission casing in a left-and-right direction normal to both the common rotation axis and the trunnion axis.
According to another aspect of the invention, a double-cavity type toroidal continuously variable transmission with two variators opposed to each other and set in tandem and coaxially arranged in an interior space of a transmission casing, each variator comprising input and output disks opposed to each other and coaxially arranged on a common rotation axis, a plurality of power rollers interposed between the input and output disks under axial preload for power transmission, a plurality of trunnions rotatably supporting the respective power rollers to permit a tilting motion of each of the power rollers about a trunnion axis perpendicular to a power-roller rotation axis for ratio changing, an upper link that mechanically links upper ends of the trunnions to each other, a lower link that mechanically links lower ends of the trunnions to each other, a link support structure that supports one of the upper and lower links in the transmission casing, the link support structure comprising a stationary portion fixed to an inner periphery of the transmission casing, and an engagement portion formed at the one link and in engagement with the stationary portion to provide an engagement pair, the engagement pair restricting a fore-and-aft movement of the one link relative to the transmission casing in a fore-and-aft direction along the common rotation axis, and a freedom for the fore-and-aft movement of the one link relative to the transmission casing being relatively less than a freedom for a vertical movement of the one link relative to the transmission casing in a vertical direction along the trunnion axis and relatively less than a freedom for a left-and-right movement of the one link relative to the transmission casing in a left-and-right direction normal to both the common rotation axis and the trunnion axis.
According to a still further aspect of the invention, a double-cavity type toroidal continuously variable transmission with two variators opposed to each other and set in tandem and coaxially arranged in an interior space of a transmission casing, each variator comprising input and output disks opposed to each other and coaxially arranged on a common rotation axis, a plurality of power rollers interposed between the input and output disks under axial preload for power transmission, a plurality of trunnions rotatably supporting the respective power rollers to permit a tilting motion of each of the power rollers about a trunnion axis perpendicular to a power-roller rotation axis for ratio changing, an upper link that mechanically links upper ends of the trunnions to each other, a lower link that mechanically links lower ends of the trunnions to each other, a link support structure that supports one of the upper and lower links in the transmission casing, the link support structure comprising a stationary portion fixed to an inner periphery of the transmission casing, and an engagement portion including a central hole, which is formed in the one link and located substantially in a middle portion of the first and second variators, an inner periphery of the central hole being in engagement with the stationary portion to provide an engagement pair, the engagement pair restricting a fore-and-aft movement of the one link relative to the transmission casing in a fore-and-aft direction along the common rotation axis, and a freedom for the fore-and-aft movement of the one link relative to the transmission casing being relatively less than a freedom for a vertical movement of the one link relative to the transmission casing in a vertical direction along the trunnion axis and relatively less than a freedom for a left-and-right movement of the one link relative to the transmission casing in a left-and-right direction normal to both the common rotation axis and the trunnion axis.